1. Field of the Invention
The present invention relates to synchronous belt systems for conveying articles, and more particularly to synchronous belt systems employing selected teeth configured to receive and house attachment fixtures for mounting to the belt a variety of conveyor transporting devices in a manner so as to not affect substantial changes to the belt's pitch line during conveying.
2. Description of Background Art
Chain and gear drive systems have been converted into conveying systems by attaching conveyor transporting devices to the chain at selected locations. Two pairs of sprocket wheels and usually a pair of continuous chains form the basic elements for a chain and gear drive system. Each chain is comprised of a plurality of equidistantly-spaced lateral rods serially linked together by pairs of linear plates swivelly affixed to the outer extremities of the rods. The spacing of the rods is such as to permit entry of a sprocket of the sprocket wheel in the region between adjacent rods promoting intermeshing of the chain with the sprocket wheels.
Such drive systems have been converted into conveying systems by attaching mounting means to either selected rods or plates enabling one to attach conveyor transporting devices at chosen locations so that articles can be brought into contact with the device on the chain and conveyed over the path of the chain during rotations of a driven intermeshing sprocket wheel.
Another conveying system has employed reinforced synchronous belts. These belts generally have a plurality of tension members or cords generally extending its length in a regimented pattern (i.e., columns of cords extending from one side edge of the belt to the other), along or near the pitch line of the belt. Integrally molded about the tension members is a resilient composition backing and a plurality of belt teeth. The backing usually has one flat surface extending the length of the belt and slightly beyond the tension members at both edges; the flat surface generally moves parallel with the path of travel of the belt. Opposite the backing, the plurality of molded teeth is disposed laterally to the longitudinally extended tension members. The molded teeth which engage the sprocket wheels of the conveying system are precisely formed and accurately spaced. The molded backing and the teeth protect the tension members from grime, oil, and moisture and from frictional wear. Thus such a belt system can be operated without the need for lubrication; and the tension members are not subject to the wear and tear exhibited by the chain of the chain drive systems.
To mount transporting devices to reinforced synchronous belts of the aforementioned type has presented problems. Transporting devices such as blocks, plates, buckets, and boxes have been adhesively fastened to the backing of such belts to convey light loads. Adhesives have been used because it has not been practical to drill holes in the belt in order to mount transporting fixtures to it.
Detachable conveyor buckets such as the one described in U.S. Pat. No. 4,248,340 of Danny L. Hild could possibly be employed on timing belt assemblies. Such a bucket is attachable and separable from a mounting bracket without the use of attachment means such as screws, bolts, and other fasteners. However, to use such a device the bracket must be affixed to the belt in a manner which would hold the bucket next to the belt at all times and particularly during translations of the belt around the circumference of the pulleys.
A major difficulty encountered by use of these prior art methods of attaching transporting devices to reinforced synchronous belts has been avoiding concentrations of stress. Since pitch lines of synchronous belts must be maintained in a neutral axis since as the belt bends around a toothed pulley, the bending pitch line is the only portion of the belt that does not change circumferential length. The belt backing material is at a larger radius from the pulley axis than the pitch line, therefore it becomes stretched as the belt bends around the pulley. As with the adhesive attachments, this stretching of the backing material puts stress on the bond joints when fixtures are adhered to the backing of the belt. An additional stress is also placed on the bond joints when the belt backing surface becomes nonplanar as the belt bends around the pulley. Consequently there are at least two parameters which limit adhering devices to the belt; namely, (1) the flexibility of the device, and (2) the longitudinal dimension of the device with respect to the pitch between the belt teeth.
Attachments to synchronous belts using headed screws or bolt-type fasteners have advantages over adhesive methods. One advantage is that the attachments are semi-permanent, allowing removal of the devices. Another advantage is that bolted devices are not prone to the same type stress failures associated with the adhesive methods. Also, a much larger variety of devices can be attached to the belts than could be attached using adhesives.
The general practice for making attachments has been to drill holes in the synchronous belt in the bottom land areas between the teeth and to use bolts routed through the drilled holes to form the belt attachments. Teeth of associated engaging pulleys are usually machined to provide clearance for the head of the fasteners. Oftimes the appropriate orientation of the belt's pitch line with respect to the pulley's pitch circle is distorted. Primary stresses associated with bolt-type fasteners are: (1) compressive stresses caused by the head of the bolt being tightened against the bottom land of the belt, and (2) contact stresses caused by the bolt's shank pressing against the wall of the mounting holes in the belt. These stresses associated with the prior bolt-type fasteners are not minimized when devices are attached in the bottom land regions of the belt.
The present invention is directed to improved techniques for forming a reinforced synchronous belt having features for attaching transporting devices which resulted from confronting and solving the basic problems as described above. In the course of the development additional unforeseen problems were resolved as will be apparent.